Laundry detergent manufacturers have attempted to meet the consumer need to rejuvenate coloured fabrics and provide good fabric-cleaning performance during the laundering process. Current fabric treatment compositions that comprise fabric-substantive dyes do not adequately clean the fabric during the laundering process, and the consumer still needs to use additional conventional laundry detergent compositions (i.e. that do not comprise fabric-substantive dyes) in order to adequately clean the fabric. However, this combination is costly and not efficient as two separate laundering processes need to be undertaken. Furthermore, previous attempts by the detergent manufacturers to provide a detergent composition that provides a good colour-rejuvenation profile have focused on dyes that are used to dye fabrics during textile mill processes, and to incorporate these dyes into laundry detergent compositions. However, these dyes are not as fabric substantive during the laundering process when relatively low temperatures (from 5° C. to 60° C.) typical of domestic laundering processes are used compared to the textile mill process when relatively higher temperatures (90° C. to 95° C.) typical of textile mill processing conditions are used. Simply incorporating these dyes into conventional laundry detergent compositions leads to inefficient colour rejuvenation profile.
Furthermore, over multiple wash cycles, the colour of fabrics laundered with conventional laundry detergent compositions deteriorates to an undesirable degree. There continues to be a need to provide a laundry detergent composition that provides good colour care, colour rejuvenation and a good cleaning performance.
The Inventors have found that the colour rejuvenation profile of solid laundry detergent composition is improved by combining a reactive dye and a detersive surfactant in a composition that has a relatively higher pH, wherein upon contact with water the composition has an equilibrium pH of 10.5 or greater at a concentration of 4 g/l in de-ionized water and at a temperature of 20° C.
Without wishing to be bound by theory, it is believed that the high pH improves the strength of the dye-fabric interaction, improves the fabric-substantivity of reactive dye and improves the colour rejuvenation profile of the solid laundry detergent composition. The inventors have found that such laundry detergent compositions provide both a good fabric-cleaning profile and a good colour-rejuvenation profile.